Thermoset resins are materials that cure to form very hard plastics. These materials can be used in a wide variety of consumer and industrial products. For example, thermosets are used in protective coatings, adhesives, electronic laminates (such as those used in the fabrication of computer circuit boards), flooring and paving applications, glass fiber-reinforced pipes, and automotive parts (including leaf springs, pumps, and electrical components). Relative to other types of plastics, cured thermosets are typically brittle. Addition of a poly(arylene ether) to a curable thermoset composition is known to decrease the brittleness of the cured resin.
For many uses, poly(arylene ether)-containing thermoset compositions must be flame retardant. For many years, halogenated flame retardants, particularly brominated flame retardants, have been added to thermoset compositions. While these halogenated flame retardants are effective, they have also been shown to bioaccumulate, and questions have been raised about their environmental and health effects. There is therefore a desire to reduce or eliminate the use of halogenated flame retardants.
Although non-halogenated flame retardants are known, many are less effective than halogenated flame retardants when compared on an equal weight basis in thermoset compositions. This means that greater amounts of the non-halogenated flame retardants must be used, and this detracts from the physical properties of the cured composition. Furthermore, some non-halogenated flame retardants, including phosphate esters, are unstable to long term use in the presence of liquid water or water vapor, and their decomposition can yield acidic products. This problem is particularly significant when the thermoset resins are used in the fabrication of printed circuit boards, because the acidic products can corrode electrical connections on the boards.
There is therefore a desire for flame retardant, poly(arylene ether)-containing thermoset compositions that avoid the use of halogenated flame retardants, exhibit high levels of flame retardancy with relatively small amounts of flame retardant additive, and avoid the generation of acidic decomposition products.